The introduction of a new material has recently changed the way of thinking in the electronics technology. Organic materials have electrical properties very similar to silicon which is doped with elements that can create regions of material with the predominance of negative electric charges (electrons) or positive charges (holes) as major carriers of the electric current, when an electric field force is applied to the terminals of the structure. The main difference between silicon and organic materials is in the scale of distances: we speak of nanometers to micrometers for silicon, while we speak of atomic to molecular distances (angstrom=1 x E-10 m) for organic materials. This difference of more than an order of magnitude makes it possible to build flexible ICs printed like paper sheets that are perfect for wearable applications for consumer electronics.
Before describing the possible scenario of applications of organic printed electronics, let’s consider the basic working principle of an organic LED (see Figure 1)
The organic diode implementation (Source: University of Wisconsin)
The electrons are emitted from the cathode (composed of Ca or Mg ) to an anode, usually a thin layer metal terminal of Indium Tin Oxide (ITO) material, by the forces of an electrical field from an external voltage applied to the Organic Light Emitting Diode (OLED). They then recombine with holes by a transition in a temporary and intermediate state of energy that comes to an end with the emission of a quantum of light, a photon that passes through the glass that is placed at the bottom part of the structure which results in the emission of light. The simultaneous recombination of more and more couples of electrons and holes implies the presence, in the organic material, of multiple emissions of photons, thus the material can be set in a state called “fluorescence”, even utilizing only a single layer of organic material.
The OLED is a very promising solution as a light emitter because of its potential of realizing a level definition of colors in an LED array display panel that cannot be reached by a normal panel of silicon LED diodes. The main reason for this exceptional definition is the possibility of high integration of more organic transparent LEDs in a stack, called TOLED (see Figure 2).
Each organic LED acts as a filter that selects a specific frequency and hence it selects a specific color; the combination of the basic colors creates a high definition image, because the organic LED technology makes it possible to place the filters very close one to each other. The light filters from one Organic LED to the next one, by crossing the transparent screen.
The cross section of a 2-TFT AMOLED pixel (Source: princeton.edu)
In the second part of this blog I will describe the scenario of possible applications of the organic and printed electronics and the market forecast figures of this very interesting technology.